Clay County, MO: EPA's radon zone, explained

EPA places Clay County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally that's the 97th percentile for radon potential — Clay County outranks 97% of every county EPA has rated.

How Clay County compares

Clay County, Missouri is home to about 263,370 people across 397.658 square miles. Population density there runs about 662 people per square mile. By population, Clay County is the 87th largest of every county sharing its EPA zone — the 92nd percentile by population within that zone. EPA's geology-based Region 7 groups Clay County with 411 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Fixing a home becomes an EPA recommendation past 4 pCi/L, and that is precisely the side of the line Clay County's Zone 1 prediction lands on, well above the roughly 1.3 pCi/L most US homes average. Some Clay County homes will test comfortably under the action level despite the county's Zone 1 rating — the only way to know which kind of home you have is an actual test.

Testing and mitigation in Clay County

For a Clay County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Missouri's state radon program

For Clay County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Clay County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

Where Clay County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Clay County's numbers. Whatever zone Clay County carries, the zone explainer covers what it does and doesn't tell you about any one house.